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PHASE II PHOSPHORUS TOTAL MAXIMUM DAILY LOADS FOR RESERVOIRS IN THE NEW YORK CITY WATER SUPPLY WATERSHED (Delaware, Dutchess, Greene, Putnam, Schoharie, Sullivan, Ulster, and Westchester Counties) June 2000 * * * * * * * * * * * * * * * * * * * * Developed in Conformance with Section 303(d) of the Clean Water Act Prepared By: New York State Department of Environmental Conservation Division of Water Bureau of Watershed Management 50 Wolf Road - Rm. 398 Albany, NY 12233-3508 PHASE II PHOSPHORUS TOTAL MAXIMUM DAILY LOADS FOR RESERVOIRS IN THE NEW YORK CITY WATER SUPPLY WATERSHED Table of Contents Page No. PHASE II TMDL PROPOSAL ...........................................3 I. WATERBODY NAME, LOCATION, BASIN .............................4 II. USE IMPAIRMENT .............................................5 III. APPLICABLE WATER QUALITY STANDARD...........................5 IV. TMDL DEVELOPMENT .........................................10 V. MONITORING ...............................................12 VI. IMPLEMENTATION\REASONABLE ASSURANCE .......................12 VII. PUBLIC PARTICIPATION........................................15 VIII. FUTURE TMDL DEVELOPMENT...................................15 IX. PHASE II TMDL SUMMARY .....................................16 X NEW YORK CITY WATER SUPPLY RESERVOIR PHASE II TMDL SUMMARIES. .21 A. CROTON RESERVOIR SYSTEM ................................21 AMAWALK RESERVOIR ........................................22 BOG BROOK RESERVOIR .......................................24 CROSS RIVER RESERVOIR ......................................25 CROTON FALLS RESERVOIR ....................................26 DIVERTING RESERVOIR ........................................27 EAST BRANCH RESERVOIR .....................................28 MIDDLE BRANCH RESERVOIR ...................................29 MUSCOOT RESERVOIR ........................................30 NEW CROTON RESERVOIR......................................32 TITICUS RESERVOIR ..........................................33 B. CATSKILL-DELAWARE RESERVOIR SYSTEM .......................34 ASHOKAN RESERVOIR....................................... .35 BOYD CORNERS RESERVOIR ....................................36 CANNONSVILLE RESERVOIR ....................................37 KENSICO RESERVOIR .........................................39 NEVERSINK RESERVOIR........................................40 PEPACTON RESERVOIR ........................................41 RONDOUT RESERVOIR ........................................42 SCHOHARIE RESERVOIR...................................... .43 WEST BRANCH RESERVOIR .....................................45 PHASE II PHOSPHORUS TOTAL MAXIMUM DAILY LOADS FOR RESERVOIRS IN THE NEW YORK CITY WATER SUPPLY WATERSHED June 2000 The New York State Department of Environmental Conservation (NYSDEC), with the cooperation and technical assistance of the New York City Department of Environmental Protection (NYCDEP) and the United States Environmental Protection Agency (USEPA), has completed its Phase II analyses of the total maximum daily loads (TMDLs) for phosphorus in the reservoirs of the New York City Water Supply Watershed (Watershed). A phased approach to the development of phosphorus TMDLs in the reservoirs in the Watershed has been selected by NYSDEC. Phase II was discussed in the Phase I TMDLs that were submitted to USEPA on January 31, 1997. Phase II TMDLs are hereby submitted to USEPA for approval. Section 303(d) of the Clean Water Act requires states to identify the waterbodies in the state which, after application of technology-based effluent limitations required by the Act, do not meet water quality standards. These waterbodies are identified as water quality limited. The Act requires the states to establish, and USEPA to approve, TMDLs which, upon implementation, will achieve the water quality standards. NYSDEC has identified the New York City Watershed reservoirs as priority waters for TMDL development for phosphorus in the 1994, 1996 and 1998 303(d) listings of waters required by the Clean Water Act. A TMDL for a pollutant is the reservoir’s loading capacity for that pollutant. A TMDL is the sum of the point source wasteload allocations (WLAs) and the nonpoint source load allocations (LAs) plus a margin of safety to account for the uncertainty in the relationship between the pollutant loads and the reservoir’s water quality. NYSDEC is applying a phased approach to establishing TMDLs for phosphorus in the New York City reservoirs. Phase I TMDLs (approved by USEPA on April 2, 1997) were initial assessments of each reservoir system to test model solutions against monitoring data. The Phase I TMDLs determined which reservoir systems had reached their loading capacity for phosphorus. Calculations of the potential reduction of phosphorus from wastewater treatment plants (WTPs), resulting from the implementation of provisions in the New York City Watershed Rules and Regulations (NYCWRR), as adopted by both NYCDEP and New York State Department of Health (NYSDOH), were provided in Phase I. Also, calculations of necessary nonpoint source reductions were provided in the Phase I TMDLs, where appropriate. - 1 ­ The Phase II analysis provides several enhancements over Phase I: 1. An accounting mechanism for phosphorus retention by the larger lakes and ponds upstream of the City’s reservoirs. 2. The use of the Generalized Watershed Loading Function (GWLF) model to estimate nonpoint source loadings of phosphorus from several land use categories. This model was applied to the Catskill and Delaware Watersheds. 3. The reservoir models used in Phase II, covered a time span of four consecutive years (1993-1996). Phase I modeled one year (1993) only. These four most recent years contain unusually wet conditions, as well as drought conditions, providing a rigorous test for the phosphorus model regarding seasonal variation. The TMDL for each reservoir is based on the geometric mean of phosphorus for growing seasons from 1992-1996. 4. The data used in the Phase II assessment of reservoir status is more recent (1992-1996) than the data set used in the Phase I assessment (1990-1994). 5. The Phase II Margin of Safety (MOS) used in the TMDL analyses has been revised to reflect the variability of phosphorus data for each reservoir. For Phase II, a factor of 10% was applied as a baseline to each reservoir to account for general uncertainty in the analysis. An additional factor was added to the 10% to account for the variability in each reservoir’s actual phosphorus data. As a result, Phase II margins of safety can range from 10 to 20 percent. In addition to the enhancements above, there has been significant effort on the part of NYCDEP toward the proposal and ultimate development of a water supply numeric criterion for phosphorus1. NYSDEC has reviewed NYCDEP’s work and determined that the adverse effects of eutrophication on the water supply have led to the development of Phase II TMDLs recognizing the following: 1. The existing New York State aesthetic-based (recreation) phosphorus guidance value of 20 FFg/L. 2. The application of the existing New York State narrative standard for phosphorus and nitrogen, and a site-specific interpretation of that standard. 1 Development of a Water Quality Guidance Value for Phase II Total Maximum Daily Loads (TMDLs) in the New York City Reservoirs; NYCDEP; March 1999. Available on the Web at: http://www.ci.nyc.ny.us/html/dep/html/tmdl.html - 2 ­ 3. NYCDEP’s distinction between source water and upstream reservoirs.1 4. The expectation that USEPA will provide guidance on eutrophication parameters. EPA’s “National Strategy for the Development of Regional Nutrient Criteria (June, 1998)” projects the establishment of nutrient criteria by the end of 2000. 5. NYSDEC’s commitment to review applicable information with regard to a site- specific phosphorus water quality standard and/or guidance value for the NYC Watershed. 6. Continued monitoring efforts that will be supported by NYSDEC and USEPA. In particular, monitoring will be linked to the upgrades currently underway at wastewater treatment facilities in the Watershed. This will assist in the assessment of point source phosphorus loads and the loading reductions accomplished. 7. Refined modeling and monitoring efforts based on Cannonsville mechanistic- type models that are being undertaken. Each reservoir basin will be subject to continued monitoring and regular assessment of phosphorus load allocations. 8. An assessment of the impacts of the recommendations made in the Putnam County and Westchester County Wastewater Diversion Studies and watershed planning efforts in the Croton or Catskill/Delaware systems when those efforts are completed. 9. USEPA’s proposed revisions to the TMDL Regulations (40CFR Part 130). 10. Implementation of nonpoint source controls assisted by the completion of Nonpoint Source Practices Report and Implementation Strategies Report. PHASE II TMDL PROPOSAL NYSDEC is presenting the following for USEPA’s approval: C Phase II TMDLs/WLAs/LAs for 9 reservoirs in the Watershed where the critical load is currently exceeded (water quality limited). C Phase II TMDLs/WLAs/LAs for 10 reservoirs in the Watershed where the critical load is currently not exceeded (effluent limited). - 3 ­ C Phase II point source phosphorus loads (WLAs2) for surface water discharges in the Watershed. These loads are developed from phosphorus effluent requirements (Section 18-36) in the NYCWRR. C Phase II nonpoint source “aggregated” phosphorus loads (LAs2) for each reservoir. All nonpoint

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